Mrs Hassan was kidnapped by a Sunni Muslim group in October 2004 and shot dead around two weeks later.

Ali Lutfi Jassar al-Rawi, also known as Abu Rasha, and Manif Slih are due to stand trial for their alleged role in taking her hostage.

The charity worker’s remains have never been found, and her siblings Deirdre, Geraldine, Kathryn and Michael Fitzsimons have battled to find them to give her a proper burial.

Their statement said: “Since Margaret’s death we have spent the last four years trying to find her remains. We have sought justice and truth, and have never given up. We want to bring her home and give her a Christian burial with the respect she deserves. This was a promise made to her by her husband (Tahseen Ali Hassan), and together with our family, he has never given up hope of fulfiling that promise.”

The family said that one of the kidnappers had tried to extort money in return for her remains.

Their statement continued: “One of these men was trying to blackmail the British Government and our family in exchange for the return of Margaret’s remains.

“He demanded money from us, and a safe haven from the British Government in the UK for his family.”

Mrs Hassan had lived in Iraq for 30 years and worked for Care International.

The family added: “We have begged them to send an Embassy official to the trial to represent our sister Margaret. They feel unable to do so because of the security situation. We do not understand this.”

The statement added: “Mr Brown said just this week that the British Government has achieved all its goals and the security situation in Iraq is much improved.”

A spokeswoman for the Foreign and Commonwealth Office refused to say whether they would send someone “for security reasons”.